I'm having 4l60 problems
 

Just bought the car it had a shift kit and all if a sudden when I put it in drive from reverse or park and it shifts hard as hell the whole car shakes

It sounds like you have a bad EPC causing it to retain high line pressure all the time. It is a fairly simple fix that can be done with the transmission in the car.

What's that? How do you fix it?

sometimes the maf will send a code and raise the line pressure to holy shit levels. my car has done it several times

+1 on this info. I meant to post this info last night and for some reason I must have forgot to after dinner! I would definitely look into this and it will more than likely fix your issues. Vince

He called yesterday afternoon and we got it all squared away. He was working on his MAF at some point and it was left unplugged.

I will never forget the time i built a trans with stock converter, super servo, trandgo HD2 kit 2 washers, 2 5/8 band.....and i forgot to plug the EPC in man you talk about a hard shifting transmission lol oh and 2nd feed was drilled to .096 lol